350 Piston

[frankfast]

Would anyone know where I might find a +1 over piston for my widecase 350 Scrambler? My barrel seems to be pitted enough to allow oil past the rings thus fouling plugs and emitting blue smoke out the exhaust. We tried running a glaze breaker through it but it would not clean it up. The cylinder was still within tolerance for a standard piston size. I know Road and Race offers them but are a bit pricey with shipping. Might there be one stateside somewhere?

[DewCatTea-Bob]

" Would anyone know where I might find a +1 over piston for my widecase 350 Scrambler?
The cylinder was still within tolerance for a standard piston size. "

____ You shouldn't need to go-with a 4th-over/77.0mm piston, cuz if a good heavy-duty hone-job doesn't quite completely clean-up your cyl.sleeve's bore-face, then the 1st-over/76.4mm piston should do the job quite well for you (without boring-out your cyl.sleeve to +1mm, all the way to the last oversize) !


Dukaddy-DUKEs,
-Bob

[frankfast]

What I meant by +1 was 1st over. I think that would be sufficient to clean up the bore quite nicely.

[frankfast]

I'm assuming that the oil is entering the cylinder past the rings because of the defects I can see in the bore. You can see them still after the honing but they are so slight that you can't feel them. Since I put new guides, seals and lapped the valves I discounted the heads as the reason oil is getting into the chamber. However it worries me that someone familiar with Singles heads suggested that since the intact tract has very little material between it and the chamber, it may be cracked. I can't see it but this would obviously be a worst case scenario. Have you had any experience with cracked heads in a Ducati Single? How would you check it if you can't see it?

[Eldert]

yes i did see cracked heads but al where converted to coil springs . i never seen a cracked head with
the original type valve springs

Eldert

[frankfast]

I too doubt that the head is cracked. There's burt oil in the exhaust port. I suspect it was pushed out of the chamber on the exhaust stroke. The guides and seals are new. I did find a piston and boring service here in the states. It's a bit pricey for my reclamation project but putting a spent Ducati Single back on the road is not a cheap proposition. I now have replaced the cam, rockers, valve guides, oil pump, and piston in the motor alone. I never considered it an investment and don't intend to sell it. Someday, I hope, my persistence will be rewarded.

[DewCatTea-Bob]

" I'm assuming that the oil is entering the cylinder past the rings because of the defects I can see in the bore. You can see them still after the honing but they are so slight that you can't feel them. "

____ If as slight as you say, then I have doubts that they're the cause.


" However it worries me that someone familiar with Singles heads suggested that since the intact tract has very little material between it and the chamber, it may be cracked. Have you had any experience with cracked heads in a Ducati Single? How would you check it if you can't see it? "

____ I've never seen any kind of head-cracks (other than in fins), in any stock DUKE-cyl.head !
__ If you still wish to check for leak-cracks, I'd suggest filling a suspected chamber with penetrating-oil or 90%-alcohol, to see if any leaks-through to be noticed elsewhere.
____ I'm thinking that your oil-smoking issue is more likely due to the oil-ring being either installed up-side-down, or broken or badly worn.
Another possibility could be that you've sometime left a petcock turned-open too long and have diluted & raised your oil-level, thus allowing your motor-oil to become burned-up easily.


Hopeful-Cheers,
-Bob

[frankfast]

Through the process of elimination, I'm pretty sure that the cylinder needs to be bored and a new piston and rings installed. The old rings were installed correctly. I think the third oil scraper ring has no top and can be installed either way, however I can barely make out a mark on it which was facing up. The second ring has a notch which faces down. The top ring has no marking. The burnt oil in the exhaust port is a sign that oil is being pushed out of the cylinder on the exhaust stroke, hence the blue smoke.
The original damage to the head because of the broken oil pump has now been fixed and oil is now flowing to the head. Boring the cylinder and a new piston and rings should get this single back on the road. Then I can start tweaking everything.

[DewCatTea-Bob]

" I'm pretty sure that the cylinder needs to be bored and a new piston and rings installed. "

____ Providing that I've correctly understood the lack of severity of the defects of your cyl.sleeve-wall, I doubt that your cyl.sleeve really "needs" to be re-bored,, cuz I've seen more than one example of severely scored cyl.walls
which had many dozens of deep -(at least .002") score-scratches on several vertical areas on the cyl.sleeve-wall, yet the DUKE-engines still ran well enough despite so,, and while such did show signs of exhaust-smoking, the smoke was not so very bad as you seem to imply that yours overly produces.
So I think you ought to first try a fresh oil-change, with an anti-smoke additive included (since the smoking is excessive enough to be an issue for you).


" Boring the cylinder and a new piston and rings should get this single back on the road. "

____ Perhaps so but, I'm thinking that that's an overly aggressive fix and an unnecessary expense at this early stage of light-malfunction. ...
I'd try another set of rings and a GOOD hone-job, before-hand.


Hopeful-Cheers,
-Bob